Treatment of wood



Paten-ted Nov. `1, 1938` PATE-Nr OFFICE TREATRENT 0F WOOD Ernest R. Boiler, Cleveland Heights, Ohio, as-

signer, by mesne assignments, to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware Application July '19,- 1935, serial No. 32,162

,a9 claims. (c1. :a1- 35) v 'Ihis invention relates to processes for depositing preservative compositions, flreproong compositions, and the like, within a porous material,

and is particularly directed to such processes' wherein such impregnating agents are carried into the porous materials in dimethyl ether.

It is now the customary practice to preserve Wood by submerging it in a water solution of a preserving salt, such as zinc chloride, and then injecting the solution into the wood by the use of pressure. After aidesired degree of penetration of the wood has been effected, the aqueous solution is ordinarily allowed to drain from the pressure receptacle. Water which is retained in the wood must subsequently be removed by kiln drying or air seasoning.

The injection of Water into the wood causes considerable swelling and, upon drying, the consequent shrinkage of the wood is attended by acertain amount of warping, checking, and raising of the grain. The extent of this deterioration of the Wood depends largely, of course,'upon the characteristics of the wood being treated and, to a lesser degree, upon the care exercised in the treating and drying-procedures. When the treated wood is to be employed in certain relations, this deterioration is not particularly disadvantageous, but wood which is warped and cheeked cannot satisfactorily be used for a large number of` The customary processes of impregnating wood by means of an aqueous vehicle have also been found disadvantageous by reason of the relatively large and expensive equipment required for 4the ordinary pressure processes. In addition to the `expense attendant upon the installation and maintenance of such equipment, there'is the additional disadvantage that the equipment is not readily adaptable to various types of wood which require modified methods of treatment.

Aqueousyehicle's o'er vetv another disadvan--' tage in that a large number of impregnating agents are not water soluble and cannot, vtherefore, be used in water solution.

Considered together, the.V above enumerated disadvantages 'have prevented the impregnation lumber with suitable agents for staining,

many commercial applications. It has been impractical to impregnate finished or semi-finished proofing, or .preserving the wood.

It hasbeen proposed to avoid the diiculties encountered when wood and the like are impregnated by the use of aqueous vehicles, by using non-aqueous menstruums. It has, for instance, been suggested. `that alcohol, or liquid hydrocarbons such as gasoline or kerosene `be used. Such non-aqueous Avehicles display the same disadvantages as do aqueousvehicles, to a greater or lesser extent, and they have the furfirether disadvantage of being quite expensive. In

addition tothe fact that the non-aqueous solvents heretofore employed are high in cost for an initial installation, their expense is rendered even greater by the fact that it is almost impossible to recover the solvent from the.p0rous material.

When wood is to be impregnated-with a preservative salt, such as zinc chloride, if a nonaqueous menstruum is tobe employed, it has been proposed to use alcoholic solutions rof zinc chloride. Alcohol causes/warping and checking of wood, though toI a' somewhat smallerv extent than does water. raising of the grain ofthe wood, and, accordingly,

like water, is unsuitable for treating finished wood.

After such a non-aqueous menstruum has been injected into wood, either/' by pressure processes or by simple immersion, it is impractical to' attempt recovery of the menstruum. course, theoretically possible to recover such nonaqueous menstruums, but the cost of such operations would be-prohibitive. In a, pressure process of impregnation, there is, of course, a certain amount of heat in the Wood, but this heat is inadequate to distill off the relatively high-boiling menstruum heretofore used. The poor heat conduction of wood, moreover, makes it impractical retained in the wood.

- Processes employing 'nomaqueous menstruums for the pressure impregnation of wood require equipment comparable in -size and cost to that used in processes employing aqueous vehicles. Processes employinghnon-aqueous menstruums also require relatively long of timev for j the impregnatlng and `drying operations. of wood by the use of an aqueous menstruum in 25.v Alcohol, moreover, causes a l It is, .of

It is 'an object of my invention to provide proc- AIl() esses which can be employed for the impregnation" of wood and the like without damage thereto. It is a further object of my invention to provide processes whereby wood may be impregnated with desired impregnating agents without the deleterious swelling, shrinking, warping, checking, and raising of the grain which attends vthe use of most of the menstruums hitherto known. A still further object of my invention is to provide processes whereby finished lumber may -satisfactorily be impregnated with suitable firel proofing, staining, and preservative agents. A

still further object of my invention is to provide processes whereby a deep and uniform penetration Aof impregnating agents can quickly and economically be achieved. A still further object of my invention is to provide processes which are low in cost, and which can readily be adapted to the condition of the Wood. Other objects of my invention will become apparent hereinafter.

My objects are accomplished, brieiiy, by impregnatingwood or the like with suitable impregnating agents carried in dimethyl ether. -The dimethyl ether may, of course, be diluted with less expensive, low boiling materials such as carbon Y dioxide.

Wood and the like may be impregnated according to the processes of my invention with'impregnating agents such asl pigments, lakes, dyes, stains, resins, gums, lacs, oils, waxes, parasiticides, and fireproong compositions. Many water insoluble impregnating agents can be dissolved in Dimethyl ether is a solventfor a wide variety of impregnating agents, but there may be found animpregnatlng agent which is not soluble theref in. In such an instance, some of the advantages of my invention may be obtained by dispersing theimpregnating agent inthe menstruum, butA it is usually desirable to employ impregnating agents which are soluble in the dimethyl ether.

The impregnation ofwood or the like may be accomplished by simply immersing itin the dimethyl etlier solution. However, it is usually preferred to inject the non-aqueous vehicle into thel wood by the use of pressure. Pressures up to the critical pressures of the dimethyl ether may be obtained by heating it. Because of the low boiling point of dimethyl ether, no large amount of heat Will be required to obtain relatively high pressures, and, under many circumstances, satisfactorily high pressures may be obtained without the additionof external heat by reason of the normal pressure of the dimethyl ether lat ordinary temperatures.

Dimethyl ether is characterized by its relatively low surface tension and its relatively low viscosity. The impregnation of wood according to the processes of-my invention, accordingly, pro-` v tank and then to the solution storage tank..

f sures, a satisfactory degree of penetration being :ceeds very rapidly even at rather moderate presobtained in a relatively short period ofv time.

"I'his, of course, is very important from an eco- Vobtained, the dimethyl ether is'drained from the wood. Afterl the liquid has been drained oil', the

liquid remaining in the wood'can readily be re f moved therefrom by permitting it to boil off.

Ordinarily, no addition of heat is necessary to effect an almost complete evaporation of the dimethyl ether, but, if desired, additional heat may besupplied. The gas which results from the boiling of the dimethyl ether can be recovered and condensed, whereupon it may be used as a k solvent for more of the impregnating agent.

It will be `apparentthat the removal of dimethyl ether is exceedingly easy of accomplishment, and it is to be noted that a substantially tical. The short time required to effect asepa- `ration of the liquid from the wood is, of course,

vder from the solution storage tank. The wood to be impregnated is placed in the treating cylinder and subjected to a vacuum, by means of complete recovery ofl the dimethyl ether is pracl the indicated vacuum pump, toremove most of v the air from the cylinder and the wood. The

cylinder is then connected to the solution storage tank, which is at a higher temperature than the cylinder, and the solution of impregnating agent flows intothe cylinder under its own pressure.

The desired temperatures and the corresponding pressures are maintained in the treating cylinder by the use of steam coils. The desired temperature and pressure are maintained for the time required to effect the desired degree of penetration of the wood. At the end of this time, the line between the treating cylinder and the solution storage tank is opened, and the solution is forced from the treating cylinder into the solution storage tank which at this time, of course, is ata lower temperature and pressure than the treating cylinder.

After the solution has been drained from the Wood and forced into the solution storage tank,

the-line between the cylinder and the solution storage tank is closed, andthe line from the treating cylinder to' the condenser is opened. The dimethyl ether which has been'retained in the wooddistills therefrom and is condensed in the condenser from which it is led to a receiving tank. The temperature of the wood is ordinarily sufficient to supply the heat required to vaporize substantially all of the menstruum.

The atmosphere of the vaporized dimethyl etherwhich remains in the treating cylinder is finally swept out with air from a blower, and dissolved in a suitable solvent, such as 60 B. sulfuric acid, in a scrubber. From time to time the returned through lthe condenser to the receiving The 'condensed liquid in the receiving tank is heated somewhat and forced, under its own pressure, through the f dissolver where a desired amount of the impregnating'y agent is put into solution'. It will be noted that a suitable storage' tank for the liquid is provided, which storage tank is equipped with heating and cooling means whereby the pressure'may'b'e adjusted.

After the dimethyl ether has been evaporated completely 2,135,030 vfrom the wood, and after any remaining gases Considering my invention with more particular reference to certain illustrative impregnating agents and certain dimethyl ether solutions, the

.following examples are given:

Example I Following the procedure above outlined, a number of samples of finished wood were subjected to a 5%- solution of. zincV chloride in dimethylxether. Temperatures of from 40 to 50 C. were maintained with corresponding pressures from 130 to 150 pounds per square inch. IIfhesel conditions were maintainedfor minutes. The woods thus treated were as follows: California white pine, heartand sap, 11/2" x 2" x 4; Wisconsin white pine, sap, 3A" x 2" x 4; 'Douglasilr, heart, 11A" x 11A x'4; red oak, heart, 3A" x 4 x 4". All of these specimens treated according `to the procedure of this example were impregnated with zinc chloride. 'I'here was'no discernible swelling, warping, or raising ofthe grain of these `iinished pieces of wood.

Example II Av cylinder of seasoned heart white oak, 31/2" in i diameter' and 4" long, was subjected to a 5% solution of zinc chloride in dimethyl ether for three hours at temperaturesof- 40 to 50 C., and at corresponding pressures of 130 to-150 pounds per square inch. The wood used in this example is practically impenetrable by aqueous solutions,

but under the conditions of this example, approximately half of fthe wood was impregnated with zinc chloride. There was no apparent swelling, checking, or distortion of the wood.

Example III Following the procedure of the above examples, a number of.. pieces of Ponderosa pine window sash were treated with a 5% solution of zinc chloride in dimethyl ether. The treatment was conducted at 150-pounds per square inch pressure'for thirty minutes for sapwood and forty` live minutes forheartwood. There was no\per ceptible swelling, warping, checking, oi' roughening of the surfaces of thewood. Examination of typical specimens 'showed complete penetration` of the wood with zinc chloride, and about one pound of zinc chloride was retained per cubic foot.

.. Example IV Following the procedure o f Example III, but using dimethyl ether containing dissolved therein about twenty per cent of carbon dioxide as the solvent for zinc chloride, a number of pieces of i iinished lumber were" impregnated. Excellent results were obtained, and it is noted that a somewhat more rapid penetration of the wood seemed to be obtained than when the dimethyl ether was used alone as a solvent.

, It will be readily understood that numerous modications may be Amade `in the above illus trative examples without departing from the spirit of my invention. Theimpregnating agent 'used and its concentration-will depend, of course,

upon the characteristics which it is desired to impart to the wood.

' The pressures of treatment may also be widely varied and they will bedetermined -for each case I- the steps comprising immersing the wood in a liquid, non-aqueous menstruum comprising diby the penetration desired, the nature of thewood, the temperature of treatment, and -the length of treatment. :When materials which can easily be impregnated are treated, itis, of course,

unnecessary to use such high pressures, and the processes of my invention may, under some circumstances, advantageously be practiced at atmospheric pressures or at pressures only slightly above atmospheric.

It willl also be understood that the scheme of operation illustrated in the accompanying drawing may be widely varied without departing from the spirit of my invention. .Instead of condensing the vaporized dimethyl ether by means of refrigeration, the gas may be condensed by the use of a compressor. It will be Vreadily, apparent, moreover, that the processes already known for the impregnation of porous and by the .use of high boiling non-aqueous menstruums may readily be adapted, according vto the teachings of my invention,`to the' use of -a'nd certain procedures and conditions of operation, it will be understood that I do notintend to be restricted thereby, the scope of my invention being apparent from the following claims:

I, claim:

1. In la 'process for the impregnation of a porous material, the step comprising immersing the material' in a liquid, non-aqueous menstruum comprising dimethyl ether, the menstruum carrying an impregnatirig agent.

2. In a .process for the impregnation of Wood, the step comprising immersing the `wood in,a liquid, non-aqueous menstruum comprising dh' methyl ether, an impregnating agent being dissolved in' the menstruum.

3. In a process for the impregnation of wood, the steps comprising immersing'the material in fa' liquid, non-aqueousk menstruum comprising `dimethyl ether, the menstruum having an impregnating agent dissolved therein, and, after impregnation of the wood, recovering the 'portion of the menstruum retained therein by volatilizing the menstruum therefrom.

4. In a process for the impregnation of wood, the step comprising immersing the wood in a liquid, non-aqueous. menstruum comprising di- Amaterials by the use of aqueous menstruums methyl ether, an impregnating agent being carried by the menstruum.

5. In a process for the impregnation of wood, the step comprising immersing the wood in a ,v liquid,- non-aqueous menstruum comprising dimethyl ether which contains dissolved carbon dioxide and a dissolved impregnatingf agent.

l 6. Ina process for the impregnation of Wood. the steps comprising treating the wood by injecting thereinto under pressurean impregnating agent dissolved in a liquid non-aqueous men- -struum' comprising dimethyl ether, and, after impregnation of the wood, recovering the portion of the menstruum retained therein'by volatilizing the-menstruum therefrom.

g '1. In a process for the impregnation' of wood,

methyl ether in which is dissolved an impregnating agnt, sealing the wood and liquid menstruum ina 'closed receptacle, raising the temperature of the menstruum to'obtain a correspending pressure-within the receptacle, withdrawing the liquid menstruum from the/reeep under pressure with an impregnating agent dissolved in a liquid, non-aqueous menstruum comprising dimethyl ether, and, after impregnation 10 of the Wood, recovering the portion of the menstruum retained therein by vclatilizing the menstruum therefrom. Y y V 9'. In a process for the impregnation of wood. the steps comprising impregnating the Wood with zinc chloride dissolved in a liquid, non-aqueous menstruum comprising dimethyl ether, and, after impregnation of the wood, recovering the portion of the menstruum retained therein by vola-v v tilizing the menstruum therefrom.

ERNEST R. BOLLER. 10 

